1. Field Of The Invention
The invention relates to sulfonated silicone polymers having improved solubility and electrical properties. It also relates to methods for synthesizing the sulfonated silicone polymers.
2. Information Disclosure
Polysiloxanes, or silicones, have received much attention as specialty polymers since their commercial application in the 1940's and are by far the most important of the inorganic backbone polymers. Interest in these systems has developed as a result of their unique properties, which include low glass transition temperatures (T.sub.g s), good thermal and oxidative stability, low surface energies, excellent biocompatibility and high gas permeabilities. There is considerable special interest in polysiloxanes that carry ionic substituents in their side chains because they offer promise as polymer electrolytes for solid state batteries and because they may provide water-soluble polymers for biomedical applications.
Zhou, Kahn and Smid [Polym. Comm. 30, 52-54 (1989)]have reported a synthesis of siloxane comb polymers with pendant sulfonate groups. A resulting polymer was reported to exhibit a glass transition temperature of -65.degree. C. and a conductivity of 10.sup.-5 ohm.sup.-1 cm.sup.-1 in the presence of one equivalent of tetraethylene glycol at 50.degree. C. The synthesis of the sulfonated silicone proceeded by opening an expoxy-functionalized silicone with Na.sub.2 S.sub.2 O.sub.5 : ##STR1##
The reaction suffers from three major drawbacks: (1) The initial polymer, before sulfonation, must be water soluble; (2) the reaction is slow, requiring a reaction time of "at least 3 days"; and (3) products are limited to those arising from epoxides.
There is thus a need for an improved synthesis of silicones bearing pendant sulfonate groups. There is also a need for improved sulfonated silicones.